1. Field of the Invention
The present invention relates to novel pentablock polymers. The pentablock polymers are biocompatible and biodegradable, and thus the pentablock polymers may be used for the administration of biologically active agents or diagnostic agents, especially hydrophilic compounds such as peptides and proteins. More particularly, this invention relates to biocompatible and biodegradable polymers useful for administering peptide or protein drugs to a subject and to a process for preparing the same. The present invention is also directed to nanoparticles and thermosensitive gels of such pentablock polymers.
2. Description of Related Art
Various block polymers are known in the art. For example, Cha et al., U.S. Pat. No. 5,702,717 discloses several triblock polymers, such as the PCL-PEG-PCL and PLA-PEG-PLA triblock polymer comprised of polyethylene glycol (“PEG”) and poly(ε-caprolactone) (“PCL”), and polylactide (“PLA”). See also Lui et al., Thermoreversible gel-sol behavior of biodegradable PCL-PEG-PCL triblock copolymer in aqueous solutions, J. Biomed. Mater. Res. B. Appl. Biomater. January 84 (1) 165-75 (2008). These polymers forming the block polymer are all well-known FDA-approved biodegradable and biocompatible materials. In addition, the pentablock polymer PLA-PCL-PEG-PCL-PLA has been studied. See Deng et al., Synthesis and Characterization of Block Polymers ofε-Caprolactone and DL-Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol), J. Polymer Sci. Vol 35 No. 4 703-708 (1997); Kim et al., The Synthesis and Biodegradable behavior of PLA-PCL-PEG-PCL-PLA Multi Block Copolymer, Polymer Preprints, Vol. 49 No. 7 1557-1558 (2000). These insoluble polymers were proposed as tissue scaffolds by Huang in a PowerPoint presentation accessed on the Internet in April 2008, Polymères Bioresorbables Dérivés de Poly(ε-caprolactone) en Ingénierie Tissulaire, Centre de Recherche surles Biopolymères Artificiels, UMR CNRS 5473 Faculté de Pharmacie, Université Montpellier I en collaboration avec Division de Bioingénierie, Université Nationale de Singapour.